Permanent tracers in producer wells have by the applicant Resman and others been proven for estimating “what flows where and how much”, i.e. which fluids flow in which parts of the well, and at which flow rates. Traditionally, different tracers have been placed in different influx zones to a production completion installed in a well. These tracers may be released as a function of downhole properties like flow velocity, by the affinity to different fluids or by mechanical devices. Topsides sampling and analysis of the concentration curves of the different tracers is used to provide information on which fluids are flowing into which zones, and may also indicate and at which rates the influx occurs in those influx zones.
In the present context, a tracer system (2) is a material unit which releases tracer molecules (3), such as a rod of moulded matrix material having tracer molecules (3) dispersed in the matrix, said tracer molecules e.g. diffusing out at an even time rate. Different Tracer Systems and different Tracer Carrier Systems for such tracer systems have been tried out, particularly polymer tracer systems arranged in parallel slot spaces around a base pipe of the completion, and the applicant has accumulated knowledge that points towards the fact that transient tracer responses created during flow transients depend on the nature of the void enveloping the tracer system, so-called delay chambers, and the venting properties of such delay chambers. In this context, a base pipe is an established term for a central pipe, usually of steel, but which may be made in other materials. The Central pipe is an inner pipe into which the production fluid enters in the production zone, and which leads downstream all the way up to topside, although there may be some rearrangement of the piping at the wellhead.